1. Field of the Invention
The present invention relates generally to a method and device for detecting a liquid level. More specifically, the invention relates to means for detection of liquid level of a liquid contained in a transparent or semi-transparent container, such as bottle.
2. Description of the Background Art
In general, in bottling of alcohols, drinks, sauces, liquid spices, it has been required to adjust the bottling amount within a predetermined range of amount. Usually, the bottling amount is controlled by controlling the liquid level in the bottle. Therefore, liquid level in the bottle has to be detected for enabling control of the bottling amount.
In one of conventional method a light source is provided at one side of a bottle at a level approximately corresponding to the desired liquid level, and a photo-receiver camera at the opposite side to and the corresponding level to the light source. The light beam is horizontally projected from the light source toward the photo-receiver camera. The photo-receiver camera receives the light beam through the bottle. The intensity of the received light beam is converted into electric voltage by means of a photoelectric transducer. This method is based on difference of light transmission factor between the bottle section containing the liquid and empty bottle section. However the border between the liquid containing section and the empty section to be detected, may become rather vague. Therefore, with such conventional device, precise detection of the liquid level cannot be performed.
In order to eliminate or reduce this drawback in the conventional process, a method and device for detecting the liquid level has been proposed, in the Japanese Patent First Publication (Tokkai). Showa No. 60-200126, published on Oct. 9, 1985. The disclosed device has a light source provided at the level below the liquid level. The light source is designed to project a diffused light beam toward the liquid surface. The photo-receiver camera is placed at a level corresponding to the standard liquid level. The photo-receiver camera is focused at the bottle surface approximately corresponding to the standard liquid level. The light beams passing through the liquid and bottle is received by the photo-receiver camera. The intensity of light beam received by the photo-receiver camera becomes high at the position of liquid level because of presence of a light beam component reflected at the rising circumferential section of the liquid surface. Therefore, output of the photelectric transducer becomes higher at the liquid level than remaining sections.
In the prior proposed system, a difficulty has arisen when the liquid is oscillating or waving. This possibly occurs during transportation through conveying system in automatic bottling processes. If the liquid is oscillating or waving, the liquid surface becomes unstable and can lead to mis-detection of the liquid level.